Presently in the field there are several different ways that closed end fasteners are used and are manufactured.
Typical applications are molding applications where the closed end is used to prevent plastic from flowing into the back side of a fastener which would fill and render the threads on the fastener un-usable. Closed end fasteners are also used in tank (fluid container) type applications to prevent fluid from escaping the tank yet provide an external attachment point for the tank. Finally, closed end fasteners are commonly used in snow board applications where the closed end is used to prevent epoxy resins from flowing into the part and filling the threads with plastics.
Presently the market place use different types of closed end fasteners. Screw machine inserts are turned to shape and may be made out of brass and sometimes steel and aluminum. The most common shape of the insert is the hex shape shown in FIGS. 1 and 1A. A drawback with brass inserts is high cost due to manufacturing time and material costs.
FIG. 1 is a view 100 of the prior art screw machine brass insert. FIG. 1A is another view 100A of the prior art screw machine brass insert resting on one of the hexagonal sides. Hexagonal head 101 of the prior art screw machine brass insert includes a tapered recess 102 leading to the threads 103 of the prior art screw machine insert. Inner threads 103 of the prior art screw machine brass insert are illustrated in FIGS. 1 and 1A. Threads 103 do not extend through the insert as illustrated in FIG. 1A. Since the threads cannot extend through the insert a longer insert must be used to obtain the required thread depth. Larger hexagonal head 104 of the prior art screw machine brass insert is illustrated in FIGS. 1 and 1A. Reference numeral 105 is the shank of the prior art screw machine brass insert.
FIG. 2 is a view 200 of the zinc die cast insert resting on flange 203F. FIG. 2A is another view 200A of the prior art zinc die cast insert shown resting on shank or barrel 201. Zinc die cast inserts are molded to shape from a zinc alloy. Zinc die cast inserts are cost prohibitive due to the cost of the molds. Further, there is considerable difficulty in plating zinc and zinc alloys to provide good corrosion resistance and lack of strength of the zinc alloys.
Still referring to FIGS. 2 and 2A, barbs or prongs 202 are illustrated protruding from shank 201. Shank 201 terminates in end portion 205. Flange 203F tapers 203T to edge 203. Reference numeral 203U denotes the underside of the flange. Inner threads 204 are illustrated in FIG. 2.
Cold headed steel parts are formed to shape then tapped. Issues with cold headed steel parts include the cost to manufacture and limitations on shapes that this manufacturing process can generate to fit different applications.
All three of these manufacturing methods have one other serious drawback. The amount of thread that can be tapped in a blind hole is limited. The hole cannot pierce through the back side of the part because it is closed and the tap must be stopped prior to bottoming out in the hole and breaking the tap in manufacturing. Due to these limitations, the length of the part must be increased to obtain the depth (amount) of thread desired.